Triangular current mode (TCM) enables the benefit of zero voltage switching, but it is accompanied by two significant functional limitations. Initially, it often requires expensive FPGA, ASIC, and/or specialized hardw...
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ISBN:
(数字)9798350351330
ISBN:
(纸本)9798350351347
Triangular current mode (TCM) enables the benefit of zero voltage switching, but it is accompanied by two significant functional limitations. Initially, it often requires expensive FPGA, ASIC, and/or specialized hardware-based sensing. Secondly, the time delays linked with such sensing and processing can lead to a trade-off between the achievable switching frequency and the precision of the triangular inductor current waveform. this paper delivers the experimental verification of an alternative method where the inductor current envelopes are measured using straightforward analog quasi-peak detectors. the sampling rate needed for these envelopes is in first approximation independent of the applied switching frequency. the control behavior is mainly unaffected by time and signal delays due to the low frequency envelope signals being used, allowing for an affordable standard DSP to implement the proposed method. Importantly, the same control loop can also facilitate continuous conduction mode (CCM) operation, whereby a normal CCM operation at constant switching frequency and a mode with variable switching frequency and constant ripple current can be featured. Using a standard two-level grid-tied inverter configuration as a case study, this paper shows a measurement based verification of the concept of the envelope tracking-based TCM (E-TCM) and CCM (E-CCM) method. A prototype is presented to demonstrate the behavior of an envelope tracking hardware solution, including a measurement-based evaluation of the proposed circuits in operation with a 0.5 kVA, two-level SiC-based converter. this converter, together with its envelope tracking circuit, is capable of operating in TCM at frequencies up to several hundred kHz and can dynamically transition to CCM during operation.
the current approach to marking attendance in colleges is tedious and time consuming. I propose AttenFace, a standalone system to analyze, track and grant attendance in real time using face recognition. Using snapshot...
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ISBN:
(数字)9781665473125
ISBN:
(纸本)9781665473132
the current approach to marking attendance in colleges is tedious and time consuming. I propose AttenFace, a standalone system to analyze, track and grant attendance in real time using face recognition. Using snapshots of class from live camera feed, the system identifies students and marks them as present in a class based on their presence in multiple snapshots taken throughout the class duration. Face recognition for each class is performed independently and in parallel, ensuring that the system scales with number of concurrent classes. Further, the separation of the face recognition server from the back-end server for attendance calculation allows the face recognition module to be integrated with existing attendance tracking software like Moodle. the face recognition algorithm runs at 10 minute intervals on classroom snapshots, significantly reducing computation compared to direct processing of live camera feed. this method also provides students the flexibility to leave class for a short duration (such as for a phone call) without losing attendance for that class. Attendance is granted to a student if he remains in class for a number of snapshots above a certain threshold. the system is fully automatic and requires no professor intervention or any form of manual attendance or even camera set-up, since the back-end directly interfaces with in-class cameras. AttenFace is a first-of-its-kind one-stop solution for face-recognition-enabled attendance in educational institutions that prevents proxy, handling all aspects from students checking attendance to professors deciding their own attendance policy, to college administration enforcing default attendance rules.
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